The present invention relates to a vibratory compaction working machine to be used for compacting backfilling soil of an excavated ditch formed below the ground surface level, and more particularly, to a machine for compacting soil placed around and above pipes for water supply and drainage, waste water, electric cables, city gas, etc. which have been laid on the bottom of the excavated ditch.
A vibratory compaction working machine of the aforementioned type have been proposed which employs a hydraulic excavator as base machine. More particularly, as shown in FIG. 1. The machine indludes a lower travel structure 1 on which an upper swing structure 2 is mounted, with the upper swing structure having a boom 3 mounted thereon for pivotal movement about a pin 5 by a hydraulic boom cylinder 4, and an arm 6 mounted on the forward end of the boom 3 for pivotal movement about a further pin 8 by a hydraulic arm cylinder 7. When it is desired to use the machine as a usual hydraulic excavator, the upper structure is further provided with an excavating bucket mounted on the forward end of the arm 6 for pivotal movement, while when it is desired to use it as a compaction working machine, a vibratory plate compactor 11 is mounted by a pin 9 applied through the fixing holes for bucket. This vibratory plate compactor 11 comprises a support bracket 13 connected via the above pin 9 to the arm 6 and connected through a further pin 10 to links 33 connected to a hydraulic bucket cylinder 12, a vibrating unit 14 attached to the bracket 13 through vibration damping and force transmitting rubber members 15, and a compacting plate 16 attached underneath the vibrating unit 14. As shown in FIG. 2, the vibratory unit 14 includes a hydraulic motor 14a and a pair of eccentric weights 14b to be driven by the motor 14a.
The vibratory compaction working machine of the conventional design as constructed above is operated as follows.
Suppose that a concrete pipe 18 of a relatively large diameter (e.g. 1 to 5 m) is laid on the bottom of a ditch 17 defined below the ground surface level (See FIG. 1), as shown in FIG. 3, a distributor 30 with a double chute 34 is operated to distribute soil 19 over at both sides of the pipe 18. Then, the boom cylinder 4, arm cylinder 7 and bucket cylinder 12 of the working machine are actuated to carry out a compaction by the compacting plate 16 of the vibratory plate compactor 11 to form a compacted soil zone of a unit thickness t measured from the bottom of the excavated ditch 17 (this unit thickness t is to be determined according to the compacting strength provided by the machine) and of a width corresponding to the width W of the compacting plate 16 (See FIG. 2B). Subsequently, the vibratory plate compactor 11 is slightly raised and the machine body (the lower travel structure and upper swing structure) is shifted a distance corresponding to the width W. The same stem of compaction is effected once again to form a further compacted soil zone with a width of W and a thickness of t, so that backfilling and compaction of a layer A is eventually performed. In this manner, similar operations are repeated for a number of layers B, C, D . . . in sequence until the combined thickness of those layers completely cover the top of the concrete pipe 18.
In this operation, there is a risk of the bucket cylinder 12 or the vibratory plate compactor 11 striking against the concrete pipe 18 when a first compaction of the layer A shown in FIG. 1 by the width W of the compacting plate 16 is completed and the vibratory plate compactor 11 is slightly raised from the layer A by slightly lifting the boom 3 by extending the boom cylinder 4. In order to avoid the risk, it will be necessary that, while the boom 3 is raised as in the direction of an arrow a in FIG. 1 by extending the boom cylinder 4, the arm 6 is pivotally moved in a direction of the arrow b by extending the arm cylinder 7. Also after the machine body is shifted a distance corresponding to the unit width w, and when the plate compactor 11 is lowered to set in a second compacting position, it will be necessary to set the plate compactor 11 in an initial position while avoiding engagement with the ditch 17 or pipe 18 by the reverse combined operation of retracting the boom cylinder 4 and the arm cylinder 7. This operation in fact is very complicated for the operator. This complicated combined operation is also necessary when the plate compactor 11 is lowered in response to or following a reduction of the soil thickness 19 or sinking of the soil that may result from the weight of the upper swing structure 2 applied to the plate compactor 11 as a downwardly-directed working forces during the compacting operation. It is noted that the unit thickness t after the sinking of each layer is several tens % less than the original thickness before compaction.
There may be involved a further problem caused from the fact that depending on the hardness of the soil material, the excavated ditch 17 may be steep or gentle in respect of its inclination and accordingly the ditch varies in width (the greater the pipe 18 becomes in diameter, this variation becomes the greater). As shown in FIG. 4, wherein a number of working positions assumed by the machine are illustrated, a width W.sub.1 which is a maximum reach of the plate compactor 11 as indicated by K, is determinable solely by the type of machine in use. Accordingly, even when backfilling and compacting an excavated ditch 17 of the same depth is performed, there is the necessity of having several machines of different capacities e.g., with shorter booms 3 and arms 6 and longer booms and arms, available for selective use.
Further, even in case the excavated ditch 17 is of a constant width, it may possibly happen that as the operation proceeds from the layer A to the layer D toward the ground surface level, the plate compactor 11 can hardly make contact with the soil adjacent the machine body because of the boom 3 and arm 6 being excessively lengthy (in FIG. 4, j indicates a working position in which the plate compactor 11 is closest to the machine body). Therefore, the zone E adjacent the upper swing structure 2 is left intact or untreated (F shows a processible zone). Accordingly, this raises a further problem in that it is necessary to employ a different machine with shorter boom 3 and arm 6, or alternatively to move the machine body rearwardly or to the left as viewed in FIG. 4 prior to resumption of the operation.
Still further, the conventional vibratory plate compactor 11, as shown in FIG. 2, includes vibration damping and force transmitting rubber members 15 mounted between the support bracket 13 and the vibrating unit 14, three on each side, fore and aft, with their axes extending perpendicularly of the axes of the pins 9, 10. When the working force is applied through the pin 10 of the link 33 as shown in FIG. 2(A), it is those members 15 situated on the right side, as viewed in the drawing, that largely resist this force, the left-hand rubber members escaping in the upward direction. Hence, the right-hand rubber members 15 deflect showing shearing and bending resistances in the vertical direction against the working force, and accordingly, the support bracket 13 is also lowered of its right-hand side toward the vibrating unit 14, so that the magnitude of the working force to be transmitted to the unit 14 as a compacting force is reduced while the compacting force tends to be exerted on the right-hand part of the compacting plate 16. This again raises the problem of difficulties in attainment of effective compaction. When, on the other hand, the boom cylinder 4 is contracted in an attempt to exert the working force upon the plate compactor 11 through the pin 9, the circumstance will be the same as that described above in that because of those rubber members 15 on the left side mainly resisting the working force, those left-hand members would deflect so that only a small magnitude of compacting force is exerted upon the compacting plate. Meanwhile, with the left side part of the compactor 11 being lowered preliminarily through the pin 9 by extending the arm cylinder 7, the working force is applied on the side of the pin 10 at the tip end of the link. Nevertheless, this will also result in a decrease in the working force transmitted to the vibrating unit 14 as a compacting force because of the right-hand rubber members being deflected.
Yet further, the vibratory compaction working machine involves another problem that follows.
When the distributor 30 is actuated to spread out soil 19 as shown in FIG. 3, such soil would be placed in the area between the periphery of the pipe 18 and the side wall of the excavated ditch 17, or somewhat closer to the periphery of the pipe 18. However, there usually is formed a vacant space X immediately below the pipe and a pile of soil as spreaded because the soil can not enter underneath the pipe 18 where load from the pipe 18 be essentially borne.
Accordingly, it is necessary to force a volume of soil into the vacant space X underneath the pipe 18 and level off the piled soil surfaces prior to carrying out the compaction work by means of the compacting plate 11. To this end, it has been common practice that with a compacting plate 16 in the form of a flat board, the compactor 11 is pivotally moved about the pin 9 in a snap action by contracting the cylinder 12, thereby forcing a volume of soil 19 into underneath the pipe 18 by the compacting plate 16 and then the volume of soil thus pushed in is compacted.
However, this operation by use of the flat compacting plate 16 proved unsatisfactory in that it is still difficult to push in the soil since that soil being pushed tends to be compacted earlier prior to being pushed in mainly because of the inclination of the plate 16 with respect to the horizontal surface being small.
An object of the invention is to provide a vibratory compaction working machine of the type which is capable of performing effective compaction in a simplified operating manner while being available for common use to excavated ditches of different widths, and which is capable of performing the same while maintaining the distance between the main structure of the machine and the excavated ditch unaltered even when the position to be compacted proceeds in sequence upwardly of the ditch.
Another object of the invention is to provide a vibratory compaction working machine of the type specified which is capable of applying sufficient thrust forces upon around the middle of a compacting plate of the vibratory plate compactor for performance of efficient compaction.
Still another object of the invention is to provide a vibratory compaction working machine of the type specified which is capable of instantly forcing a volume of soil into underneath a pipe to be laid under the ground and compacting the same soil.